Modulation of MUC7 mucin expression by exogenous factors in airway cells in vitro and in vivo

MUC7 VNTR polymorphism and association with bronchial asthma in Egyptian children

Overproduction of mucins in the airways donates largely to airway blockage in asthma patients. Glycoprotein MUC7 plays a role in the clearance of bacteria and has anti-candidacidal criteria. Our goal was to investigate the association between the MUC7 variable number of tandem repeats (VNTR) polymorphism and bronchial asthma among Egyptian children. The MUC7 VNTR polymorphism was investigated among 100 children with bronchial asthma and 100 healthy controls using polymerase chain reaction (PCR) method. Serum levels of immunoglobulin E (IgE), tumor necrosis factor-alpha (TNF-α), and transforming growth factor-beta1 (TGF-β1) were assessed by enzyme-linked immunosorbent assay (ELISA) technique. The frequencies of 6*5 genotype, 5*5 genotype, (6*5 + 5*5) genotypes, and MUC7*5 allele of the MUC7 VNTR variant were significantly lower among asthmatic patients than controls (p < 0.015, OR = 0.39, 95% CI = 0.19-0.81; p = 0.03, OR = 0.18, 95% CI = 0.04-0.86; p < 0.001, OR = 0.29, 95% CI = 0.15-0.58; p < 0.001, OR = 0.3, 95% CI = 0.17-0.55, respectively). The (6*5 + 5*5) genotypes of the MUC7 VNTR variant were not associated with the clinical manifestations and serum levels of IgE, TNF-α, and TGF-β1 among asthmatic patients (p ˃ 0.05). In conclusion, the (6*5 + 5*5) genotypes of the MUC7 VNTR variant may have a protective role for bronchial asthma in Egyptian children.

Aberrant MUC1 accumulation in salivary glands of Sjögren’s syndrome patients is reversed by TUDCA in vitro

Objectives

Xerostomia in SS patients has been associated with low quality and quantity of salivary mucins, which are fundamental for the hydration and protection of the oral mucosa. The aim of this study was to evaluate if cytokines induce aberrant mucin expression and whether tauroursodeoxycholic acid (TUDCA) is able to counteract such an anomaly.

Methods

Labial salivary glands from 16 SS patients and 15 control subjects, as well as 3D acini or human submandibular gland cells stimulated with TNF-α or IFN-γ and co-incubated with TUDCA, were analysed. mRNA and protein levels of Mucin 1 (MUC1) and MUC7 were determined by RT-qPCR and western blot, respectively. Co-immunoprecipitation and immunofluorescence assays for mucins and GRP78 [an endoplasmic reticulum (ER)-resident protein] were also performed. mRNA levels of RelA/p65 (nuclear factor-κB subunit), TNF-α, IL-1β, IL-6, SEL1L and EDEM1 were determined by RT-qPCR, and RelA/p65 localization was evaluated by immunofluorescence.

Results

MUC1 is overexpressed and accumulated in the ER of labial salivary gland from SS patients, while MUC7 accumulates throughout the cytoplasm of acinar cells; however, MUC1, but not MUC7, co-precipitated with GRP78. TUDCA diminished the overexpression and aberrant accumulation of MUC1 induced by TNF-α and IFN-γ, as well as the nuclear translocation of RelA/p65, together with the expression of inflammatory and ER stress markers in 3D acini.

Conclusion

Chronic inflammation alters the secretory process of MUC1, inducing ER stress and affecting the quality of saliva in SS patients. TUDCA showed anti-inflammatory properties decreasing aberrant MUC1 accumulation. Further studies are necessary to evaluate the potential therapeutic effect of TUDCA in restoring glandular homeostasis in SS patients.

Genetically engineered mucin mouse models for inflammation and cancer

Mucins are heavily O-glycosylated proteins primarily produced by glandular and ductal epithelial cells, either in membrane-tethered or secretory forms, for providing lubrication and protection from various exogenous and endogenous insults. However, recent studies have linked their aberrant overexpression with infection, inflammation, and cancer that underscores their importance in tissue homeostasis. In this review, we present current status of the existing mouse models that have been developed to gain insights into the functional role(s) of mucins under physiological and pathological conditions. Knockout mouse models for membrane-associated (Muc1 and Muc16) and secretory mucins (Muc2) have helped us to elucidate the role of mucins in providing effective and protective barrier functions against pathological threats, participation in disease progression, and improved our understanding of mucin interaction with biotic and abiotic environmental components. Emphasis is also given to available transgenic mouse models (MUC1 and MUC7), which has been exploited to understand the context-dependent regulation and therapeutic potential of human mucins during inflammation and cancer.

Investigation of the N-terminal coding region of MUC7 alterations in dentistry students with and without caries

Human low-molecular weight salivary mucin (MUC7) is a small, secreted glycoprotein coded by MUC7. In the oral cavity, they inhibit the colonization of oral bacteria, including cariogenic ones, by masking their surface adhesions, thus helping saliva to avoid dental caries. The N-terminal domain is important for low-molecular weight (MG2) mucins to contact with oral microorganisms. In this study, we aimed to identify the N-terminal coding region of the MUC7 gene between individuals with and without caries. Forty-four healthy dental students were enrolled in this study; 24 of them were classified to have caries [decayed, missing, filled-teeth (DMFT) = 5.6] according to the World Health Organization (WHO) criteria, and 20 of them were caries-free (DMFT = 0). Simplified oral hygiene index (OHI-S) and gingival index (GI) were used to determine the oral hygiene and gingival conditions. Total protein levels and salivary total protein levels and salivary buffer capacity (SBC) were determined by Lowry and Ericsson methods. DNA was extracted from peripheral blood cells of all the participants and genotyping was carried out by a polymerase chain reaction (PCR)-sequencing method. No statistical differences were found between two groups in the terms of salivary parameters, oral hygiene and gingival conditions. We detected one common single nucleotide polymorphism (SNP) that leads to a change of asparagine to lysine at codon 80. This substitution was found in 29.0 and 40.0%, respectively, of the groups with and without caries. No other sequence variations were detected. The SNP found in this study may be a specific polymorphism affecting the Turkish population. Further studies with extended numbers are necessary in order to clarify this finding.

Metabolism and Pathogenicity of Pseudomonas aeruginosa Infections in the Lungs of Individuals with Cystic Fibrosis

Individuals with the genetic disease cystic fibrosis (CF) accumulate mucus or sputum in their lungs. This sputum is a potent growth substrate for a range of potential pathogens, and the opportunistic bacterium Pseudomonas aeruginosa is generally most difficult of these to eradicate. As a result, P. aeruginosa infections are frequently maintained in the CF lung throughout life, and are the leading cause of death for these individuals. While great effort has been expended to better understand and treat these devastating infections, only recently have researchers begun to rigorously examine the roles played by specific nutrients in CF sputum to cue P. aeruginosa pathogenicity. This chapter summarizes the current state of knowledge regarding how P. aeruginosa metabolism in CF sputum affects initiation and maintenance of these infections. It contains an overview of CF lung disease and the mechanisms of P. aeruginosa pathogenicity. Several model systems used to study these infections are described with emphasis on the challenge of replicating the chronic infections observed in humans with CF. Nutrients present in CF sputum are surveyed, and the impacts of these nutrients on the infection are discussed. The chapter concludes by addressing the future of this line of research including the use of next-generation technologies and the potential for metabolism-based therapeutics.

Aberrant expression of mucin core proteins and o-linked glycans associated with progression of pancreatic cancer

PURPOSE

Mucin expression is a common feature of most adenocarcinomas and features prominently in current attempts to improve diagnosis and therapy for pancreatic cancer and other adenocarcinomas. We investigated the expression of a number of mucin core proteins and associated O-linked glycans expressed in pancreatic adenocarcinoma-sialyl Tn (STn), Tn, T antigen, sialyl Lewis A (CA19-9), sialyl Lewis C (SLeC), Lewis X (LeX), and sialyl LeX (SLeX)-during the progression of pancreatic cancer from early stages to metastatic disease.

EXPERIMENTAL DESIGN

Immunohistochemical analyses of mucin and associated glycan expression on primary tumor and liver metastatic tumor samples were conducted with matched sets of tissues from 40 autopsy patients diagnosed with pancreatic adenocarcinoma, 14 surgically resected tissue samples, and 8 normal pancreata.

RESULTS

There were significant changes in mucin expression patterns throughout disease progression. MUC1 and MUC4 were differentially glycosylated as the disease progressed from early pancreatic intraepithelial neoplasias to metastatic disease. De novo expression of several mucins correlated with increased metastasis indicating a potentially more invasive phenotype, and we show the expression of MUC6 in acinar cells undergoing acinar to ductal metaplasia. A "cancer field-effect" that included changes in mucin protein expression and glycosylation in the adjacent normal pancreas was also seen.

CONCLUSIONS

There are significant alterations in mucin expression and posttranslational processing during progression of pancreatic cancer from early lesions to metastasis. The results are presented in the context of how mucins influence the biology of tumor cells and their microenvironment during progression of pancreatic cancer.

Humanized mouse model used to monitor MUC gene expression in nasal polyps and to preclinically evaluate the efficacy of montelukast in reducing mucus production

OBJECTIVES

To determine whether MUC gene expression could be down-regulated in nasal polyps by the leukotriene receptor antagonist montelukast, we developed a system in which nondisrupted human nasal polyps could be successfully implanted into severely immunocompromised mice, and in which the histopathology of the original nasal polyp tissue could be preserved for long periods. In addition, the histopathologic changes in the human nasal polyps were carefully examined to determine the origin of the submucosal glands (SMGs) that develop in true nasal polyps found in the anterior third of the nose.

METHODS

Small, nondisrupted pieces of human nasal polyp tissues were subcutaneously implanted into NOD-scid IL-2rgamma(null) mice. Xenograft-bearing mice were treated with either montelukast or saline solution. Xenografts at 8 to 12 weeks after implantation were examined histologically, and expression of MUC genes 4, 5AC, and 7 was studied in the polyps before implantation and in the 8-week xenograft. Alzet pumps were inserted into the mice, and montelukast (Singulair) was continuously delivered to determine its effect on goblet cell hyperplasia, mucus production, and the enlargement of nasal polyps over an 8-week period.

RESULTS

The xenografts were maintained in a viable and functional state for up to 3 months and retained a histopathology similar to that of the original tissue, but with a noticeable increase in goblet cell hyperplasia and marked mucus accumulation in the SMGs. MUC4 and MUC5AC were significantly increased in the xenograft 8 weeks after implantation, but MUC7 was significantly decreased compared to the preimplantation polyps. Inasmuch as MUC7 is found exclusively in serous glands, the findings suggest that serous glands are not found in polyps in the anterior third of the nose. The histopathologic findings confirm the original findings of Tos et al suggesting that the SMGs are derived from pinching-off of the epithelium of the enlarging polyp following inflammatory changes. These SMGs have the same epithelium as surface epithelium and consist of multiple goblet cells that secrete periodic acid Schiff stain-positive mucin into the interior of the SMGs. A progressive increase in the volume of the xenografts was observed, with little or no evidence of mouse cell infiltration into the human leukocyte antigen-positive human tissue. An average twofold increase in polyp volume was found 2 months after engraftment. Montelukast did not decrease the growth of the xenograft in the 8-week NOD-scid mice, nor did it affect MUC gene expression.

CONCLUSIONS

The use of innate and adaptive immunodeficient NOD-scid mice homozygous for targeted mutations in the IL-2 gamma-chain locus NOD-scid IL-2r gamma(null) for establishing engraftment of nondisrupted pieces of human nasal polyp tissues represents a significant advancement in studying chronic inflammation over a long period of time. In the present study, we utilized this humanized mouse model to confirm our prediction that MUC genes 4 and 5AC are highly expressed and significantly increased over those of preimplanted polyps. The overexpression of these 2 MUC genes correlates with both the goblet cell hyperplasia and the excessive mucus production that are found in nasal polyp xenografts. MUC7, which is primarily associated with the submucosa, as opposed to MUC4 and MUC5AC, which are primarily expressed in the epithelium, was significantly decreased in the nasal polyp xenografts. Montelukast had no significant effect on MUC gene expression in the xenografts. In addition to the MUC gene expression patterns, the histology of the xenografts supports the concept that mucinous glands that are characteristic of true nasal polyps are significantly different from those in the mucosa found in the lateral wall of the nose in patients with chronic sinusitis without nasal polyps. The mucinous glands seen in nasal polyps (which appear to be derived from an invagination of hyperplastic epithelial mucosa containing large numbers of goblet cells) are histologically distinct from the seromucinous glands found in the submucosa of hyperplastic middle turbinates. The data presented here establish a humanized mouse model as a viable approach to study nasal polyp growth, to assess the therapeutic efficacy of various drugs in this chronic inflammatory disease, and to contribute to our understanding of the pathogenesis of this disease.

Regulation of Human MUC7 Mucin Gene Expression by Cigarette Smoke Extract or Cigarette Smoke and Pseudomonas aeruginosa Lipopolysaccharide in Human Airway Epithelial Cells and in MUC7 Transgenic Mice

Objective:

The human MUC7 gene encodes a low-molecular-weight mucin glycoprotein that functions in lubrication/protection of epithelial surfaces of the oral cavity and respiratory tract. This study was designed to evaluate the effect of cigarette smoke extract (CSE), cigarette smoke (CS), and Pseudomonas aeruginosa lipopolysaccharide (LPS), either alone or in the combination, on MUC7 expression in vitro and in vivo.

Materials and Methods:

qRT-PCR was used to determine the levels of mucin gene transcription in the human lung carcinoma cell line NCI-H292 (in vitro) and MUC7 transgenic mouse tissues (in vivo). ELISA was used to assess mucin glycoprotein levels in the cell line, and immunohistochemistry to assess mucins in lung and trachea sections.

Results:

In vitro treatment of cells with LPS (10 (µg/ml) or CSE (0.5, 1, 2.5 and 5%) alone, resulted in a statistically significant increase of MUC7 transcripts only with 1%CSE (3.2-fold). The combined CSE/LPS treatment resulted in a synergistic increase of MUC7 with 0.5%CSE/LPS (4.4 fold). MUC7 glycoprotein levels increased only minimally, the highest increase was seen with the 0.5%CSE/LPS combination treatment (1.3-fold). In vivo exposure of MUC7 transgenic mice to CS, LPS or CS/LPS combination resulted in significant increase in MUC7 transcripts only with LPS treatment (in both trachea and lung). Immunohistochemistry indicated variable increase in MUC7 glycoprotein with CS and LPS treatment, both in the trachea and lungs, but CS/LPS exposure appeared to yield the highest increase.

Conclusion:

In vitro, CSE and a combination of CSE/LPS treatment upregulated MUC7 gene transcription. In vivo, LPS upregulated MUC7 transcription, and a combination of CS/LPS appeared to increase MUC7 glycoprotein.

Current status of mucins in the diagnosis and therapy of cancer

Mucins are the most abundant high molecular weight glycoproteins in mucus. Their nature and glycosylation content dictates the biochemical and biophysical properties of viscoelastic secretions, pointing out an important role in diverse biological functions, such as differentiation, cell adhesions, immune responses, and cell signaling. Mucins are expressed in tubular organs by specialized epithelial cells in the body. Their aberrant expression is well documented in a variety of inflammatory or malignant diseases. From a prognosis point of view, their expression and alterations in glycosylation are associated with the development and progression of malignant diseases. Therefore, mucins can be used as valuable markers to distinguish between normal and disease conditions. Indeed, this alteration in glycosylation patterns generates several epitopes in the oligosaccharide side chains that can be used as diagnostic and/or prognostic markers. Furthermore, these characteristic tumor-associated epitopes are extensively used as appropriate immunotargets of malignant epithelial cells. Therefore, in an effort to detect and treat cancer at the earliest stage possible, mucins are analyzed as potential markers of disease for diagnosis, progression, and for therapeutic purposes. In this review, we focused on the current status of the distribution of mucins in normal and pathologic conditions and their clinical use both in cancer diagnosis and therapeutics treatments.

Distribution of mucins and antimicrobial substances lysozyme and lactoferrin in the laryngeal subglottic region

The subglottic region of the larynx is of high clinical relevance with regard to infections and malignancies. Little is known about the distribution of mucins and antimicrobial substances in this area. In this study, we have investigated the mucin distribution in the normal subglottis of the larynx. Moreover, we analysed the expression of lysozyme and lactoferrin in this area. Therefore, the subglottic region of 34 larynges was investigated immunohistochemically with different antibodies to mucins and antimicrobial substances. The epithelium reacted positive with antibodies to mucins MUC1 (34/34), 5AC (26/34), 5B (10/34), 7 (8/34), 8 (10/34) and 16 (19/34); submucosal glands were positive to mucins MUC1 (34/34), 5B (10/34), 7 (8/34), and 16 (19/34); high columnar epithelial cells and serous parts of subepithelial seromucous glands were also positive for lysozyme (34/34) and lactoferrin (34/34). The results show that human subglottic epithelium and subepithelial submucosal glands produce a broad spectrum of mucins that is almost comparable with that in other areas of the respiratory tract. We hypothesize that the mucin diversity of the subglottis has an impact on positive functional consequences during vocal production and antimicrobial defence. This antimicrobial defence is supported by synthesis and secretion of antimicrobial substances such as lysozyme and lactoferrin. Moreover, knowledge of the observed distribution pattern of mucins in the subglottis can be a useful tool for a classification of subglottic laryngeal carcinomas.

Regulation of airway mucin gene expression

Mucins are important components that exert a variety of functions in cell-cell interaction, epidermal growth factor receptor signaling, and airways protection. In the conducting airways of the lungs, mucins are the major contributor to the viscoelastic property of mucous secretion, which is the major barrier to trapping inhaled microbial organism, particulates, and oxidative pollutants. The homeostasis of mucin production is an important feature in conducting airways for the maintenance of mucociliary function. Aberrant mucin secretion and accumulation in airway lumen are clinical hallmarks associated with various lung diseases, such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, emphysema, and lung cancer. Among 20 known mucin genes identified, 11 of them have been verified at either the mRNA and/or protein level in airways. The regulation of mucin genes is complicated, as are the mediators and signaling pathways. This review summarizes the current view on the mediators, the signaling pathways, and the transcriptional units that are involved in the regulation of airway mucin gene expression. In addition, we also point out essential features of epigenetic mechanisms for the regulation of these genes.

Mucins in the mucosal barrier to infection

The mucosal tissues of the gastrointestinal, respiratory, reproductive, and urinary tracts, and the surface of the eye present an enormous surface area to the exterior environment. All of these tissues are covered with resident microbial flora, which vary considerably in composition and complexity. Mucosal tissues represent the site of infection or route of access for the majority of viruses, bacteria, yeast, protozoa, and multicellular parasites that cause human disease. Mucin glycoproteins are secreted in large quantities by mucosal epithelia, and cell surface mucins are a prominent feature of the apical glycocalyx of all mucosal epithelia. In this review, we highlight the central role played by mucins in accommodating the resident commensal flora and limiting infectious disease, interplay between underlying innate and adaptive immunity and mucins, and the strategies used by successful mucosal pathogens to subvert or avoid the mucin barrier, with a particular focus on bacteria.

Pathobiology of cigarette smoke-induced chronic obstructive pulmonary disease

Chronic obstructive pulmonary diseases (COPD), comprised of pulmonary emphysema, chronic bronchitis, and structural and inflammatory changes of small airways, is a leading cause of morbidity and mortality in the world. A better understanding of the pathobiology of COPD is critical for the developing of novel therapies, as the majority of patients with the disease have little therapeutic options at the present time. The pathobiology of COPD encompasses multiple injurious processes including inflammation (excessive or inappropriate innate and adaptive immunity), cellular apoptosis, altered cellular and molecular alveolar maintenance program, abnormal cell repair, extracellular matrix destruction (protease and anti-protease imbalance), and oxidative stress (oxidant and antioxidant imbalance). These processes are triggered by urban and rural air pollutants and active and/or passive cigarette smoke and modified by cellular senescence and infection. A series of receptor-mediated signal transduction pathways are activated by reactive oxygen species and tobacco components, resulting in impairment of a variety of cell signaling and cytokine networks, subsequently leading to chronic airway responses with mucus production, airway remodeling, and alveolar destruction. The authors provide an updated insight into the molecular and cellular pathobiology of COPD based on human and/or animal data.

Functional analysis of human MUC7 mucin gene 5'-flanking region in lung epithelial cells

The human MUC7 gene encodes a low-molecular-mass mucin glycoprotein that functions in modulation of microbial flora in the oral cavity and respiratory tracts. MUC7 gene expression is tissue- and cell-specific, with dominant expression in salivary gland acinar cells. To begin to understand the molecular mechanisms responsible for controlling MUC7 gene expression, we analyzed the promoter activity of MUC7 5'-flanking region in a human lung epithelial cell line A549. We demonstrated that MUC7 gene is expressed constitutively in this cell line and is upregulated by TNF-alpha stimulation. The promoter activities of a 2,762-bp fragment of the human genomic DNA (-2,732/+30 bp) and its deletion series, subcloned into a luciferase reporter vector, were characterized at the basal level and under stimulation by TNF-alpha. The results indicated that the minimal functional MUC7 promoter is in the region of -138/+30 bp. This region also revealed the greatest increase in the promoter activity upon TNF-alpha stimulation. Two putative AP1-binding elements and one NF-kappaB-binding element were identified within the proximal promoter. Further analyses demonstrated that mutations of these elements dramatically reduced specific DNA-protein binding ability and reporter gene expression. AP1 elements played an essential role in the constitutive expression, while the NF-kappaB element was crucially important in the response to TNF-alpha stimulation, demonstrating that TNF-alpha activates MUC7 transcription via NF-kappaB signaling pathway.